National concern about our heavy dependence on energy supplies from unreliable overseas sources has generated widespread interest in alternative energy supplies from domestic sources. Coal is our principal domestic energy source, and is being more widely utilized in stationary energy plants, such as for electric power generation. But efforts to use coal as an energy source for our critical transportation industry have been disappointing.
In a coal fired steam electric plant, the coal combustion products do not pass though the power generating steam turbine. But in the internal combustion engines, used for transportation power, the fuel combustion products are the working fluid inside the power producing engine, whether piston engine or gas turbine engine, and the combustion products from coal, such as ashes, create engine wear problems. Railroad diesel engines operated on slurry fuels of finely divided coal particles, suspended in water, ran satisfactorily, but experienced increased ring and liner wear, and severe fuel injection nozzle wear. These extensive experiments are summarized in the referenced, “Coal Fueled Diesel Engines,” 1993, J. Caton and H. Webb, ASME Publication ICE-Vol 19. The piston engine described in U.S. Pat. No. 4,412,511, Firey, 1983, sought to avoid these ash wear problems by burning the coal as chunks, in a separate combustion chamber, from which the ashes were separately removed, thus avoiding ash contact with the engine pistons and cylinders. To secure sufficient coal chunk surface area, for adequate coal burning rate, a large coal combustion chamber was required. The consequent low engine compression ratio created a low fuel efficiency.
United States coal reserves are very large, having approximately ten times the energy content of worldwide petroleum reserves. Indeed, worldwide coal reserves have approximately thirty times the energy content of worldwide petrol reserves. Clearly our national effort to achieve energy independence would be greatly facilitated if internal combustion engines were available, for our transportation industry, which could operate on coal or coal derived fuel.